Bathymetry

Bathymetry is the study of how deep the water is in oceans, rivers, and lakes. It helps us learn about the shape and features of the ground under the water, just like how we study the land above water. People have been measuring water depths for thousands of years, with the first records coming from Ancient Egypt.

Bathymetry is important because it helps us make special maps called bathymetric charts. These charts show where it is safe for ships to travel and point out places where the water might be too shallow or have tricky terrain. They also help scientists learn about sea creatures that live near the bottom and study how water moves in oceans.

To measure depths, scientists use different tools such as depth sounding, sonar, and satellite technology. Even with all these tools, much of the ocean floor is still not as well known as the surface of Mars. These measurements help us understand our underwater world better and keep people safe while traveling or studying the water.

Seabed topography

Bathymetry is the study of how deep the ocean, river, or lake beds are. It helps us learn about the shape and features of the ground under the water, just like how we study the land above water. People have been measuring water depths for thousands of years, with the first records coming from Ancient Egypt.

Measurement

See also: Hydrographic survey § Methods

Long ago, people measured the depth of the ocean by lowering a heavy rope or cable from a ship. This method could only measure one spot at a time and was not very quick or exact.

Today, we use special tools called echosounders on boats. These tools send out sound waves that bounce off the seafloor and return, showing us how deep the water is. We can also use satellite pictures and airplane sensors to study the ocean floor from above.

In the early 1930s, simple sounders were used. Now, we often use advanced tools called multibeam echosounders. These tools send out many narrow beams of sound at once, covering a wide area quickly and giving very detailed maps of the seafloor.

Satellites can also help us study the ocean floor. They look at small changes in the ocean's surface that happen because of underwater mountains and valleys.

In the United States, groups like the United States Army Corps of Engineers and the National Oceanic and Atmospheric Administration are in charge of measuring and mapping waterways.

Occupations or careers related to bathymetry include the study of oceans, underwater rocks and minerals, and underwater earthquakes or volcanoes. Taking and studying bathymetric measurements is an important part of hydrography, which helps keep shipping safe around the world.

Satellite imagery

Further information: Satellite imagery and Satellite-derived bathymetry

We can also map the seafloor using satellites equipped with special sensors. These sensors take constant pictures of coastal areas, helping us see the seafloor from space.

Hyper-spectral sensors

Main article: Hyperspectral imaging

Hyper-spectral sensors collect data in many different colors. This helps scientists study things like tiny plants in the water, salt levels, and dirt in the water. However, it does not give us very clear pictures of the seafloor.

Multi-spectral sensors

Main article: Multispectral imaging

Multi-spectral sensors look at fewer colors than hyper-spectral sensors but cover larger areas. This makes it easier to see general features of the seafloor in the pictures they take.

Airborne laser bathymetry

Main article: Airborne lidar bathymetry

A modern way to map the seafloor from the air uses lasers. This method, called airborne laser bathymetry, sends out light pulses from airplanes to measure the distance to the seafloor. It can see both the surface of the water and the bottom below.

Examples of commercial LIDAR bathymetry systems

There are different LIDAR bathymetry systems available for use. Two of these are the Scanning Hydrographic Operational Airborne Lidar Survey (SHOALS) and the Laser Airborne Depth Sounder (LADS).

High resolution orthoimagery

Further information: Orthophoto

High resolution orthoimagery creates images that show the true shape and angle of objects. These corrected images, called orthoimages, are used to make detailed maps of areas on land.

History

See also: Bathymetric chart § History

People have measured ocean depths for thousands of years. The ancient Egyptians used a long pole to feel the bottom of the water around 1800 BCE. Later, they used a heavy line with marks to show the depth. These early ways could only tell the depth at one spot and were hard to use in rough water.

In the 1870s, a big ship called HMS Challenger helped scientists measure deeper parts of the ocean using special wires and winches. In the 1920s, new tools called echo sounders used sound waves to find the seafloor. By the 1950s, scientists like Marie Tharp and Bruce Charles Heezen made detailed maps of the ocean bottom. Today, we use satellites and advanced tools to learn even more about the shape of the ocean floor.

Charts

This section shows charts and maps that help us see how deep the ocean, rivers, and lakes are. These charts are like maps of the underwater world. They show the shape and depth of the seafloor, riverbeds, and lakebeds. They help scientists and explorers learn more about what is under the water.